1. Field
Embodiments of the present disclosure generally relate to methods and apparatus for forming a semiconductor device. More specifically, embodiments described herein relate to a chemical vapor deposition (CVD) oxide surface preconditioning process.
2. Description of the Related Art
In semiconductor fabrication, oxide fabrication is critical, especially for thin layer oxides which is an essential part of gate structure for Complimentary Metal Oxide Semiconductor (CMOS) technology. With proper manufacturing control, oxide layers exhibit stable and desirable dielectric properties. A variety of oxide fabrication processes are used in integrated device manufacturing (IDM) to obtain oxides of different properties for different functions. Thermal oxides and deposited oxides are most commonly used in semiconductor devices. Additionally, native oxides may be generated during processing. Different oxides may also respond differently to subsequent processes and may require different treatment for the same purpose.
A native oxide typically forms when a substrate surface is exposed to oxygen. Oxygen exposure occurs when substrates are moved between processing chambers at atmospheric conditions, or when a small amount of oxygen remains in a vacuum chamber. Native oxides may also result from contamination during etching processes. Native oxides are typically undesirable and need to be removed prior to a subsequent processing.
During semiconductor fabrication, structures may be formed with excess material and then etched and/or polished back to a desired dimension. For oxide features, polishing and etching are generally used after formation to reach a desired size. Some oxide features may have two or more oxides that respond differently to the same process, hence posing difficulties in processing, especially at advanced technology nodes, such as sub-10 nm nodes.
Shallow Trench Isolation (STI) is one of the oxide structures that have several forms of oxides. STI is a form of device isolation technology used for sub-0.25 micron fabrication. Oxide filled trenches are used to isolate devices formed on a semiconductor substrate. Trenches are first etched on a semiconductor substrate, followed by growth or deposition of an oxide layer. A chemical mechanical polishing (CMP) process may be performed on the oxide filled trench after deposition, followed by an etching process to prepare the trench and other structures on the substrate for the subsequent process, such as various well implants, gate oxidation, deposition, and patterning.
Sputter etching processes and wet etching processes are conventional oxide etching processed used in STI etching. However, sputter etching processes generally cannot completely remove oxides and can damage delicate silicon layers by physical bombardment. Wet etching utilizes chemical solutions, for example hydrofluoric acid (HF) and deionized water, to remove oxides. However, diluted HF has the disadvantage of having a variable oxide etch rate. Various types of oxides have varying etch rates depending on the type of etching process utilized. Thus, significant variability and integration issues may persist when removing oxides.
Moreover, maintaining desired critical dimensions of features formed on the substrate is important to manufacture defect free semiconductor devices. Various oxide etching processes may not be suitable for maintaining necessary critical dimension which may lead to an excess degree of critical dimension increase, or blow-out. Further, various etching processes may not provide substrate surfaces for subsequent processing operations.
Therefore, there is a need for apparatus and methods for conditioning and cleaning substrate and oxide features formed on a substrate.